A Freakonomics podcast interviewed Prof. Melissa Kearney. Her thesis was that better jobs would result in more marriages in the USA. As an economist this was important to her because kids with married parents do better than other kids.
The data showed that her thesis was wrong. The marriage rate did not increase although the number of kids in traditional families did go up.
It is obvious that culture is the obvious key to having more couples marry. There are many economically poor places that have lots of marriages. Bnei Brak, Israel is one example.
It seems like a stable, thriving society needs good traditional families. The best way of achieving this may be religion.